Weapons of Mass Infections Flashcards
Primary Pathogens
-cause disease in healthy hosts
Opportunistic Pathogens
-cause disease only in compromised hosts or entry into unprotected sites
-generally do not cause trouble, but will take over if opportunity presents itself.
Infection
-when a pathogen or parasite enters/begins to grow on a host
-doesn’t imply overt disease
-some microbes can enter latent state during infection, prevent them from being found on culture
Pathogenicity
-organism’s ability to cause disease
-defined in terms of:
–infectivity (how easy it causes disease)
–virulence (how severe that disease is)
–specific genetic makeup of pathogen
Virulence
-relative ability of pathogen to cause disease
-measured with ID50 (infectious dose) & LD50 (lethal dose)
ID50
-# of pathogen cells or virions required to cause active infection in 50% of inoculated animals
LD50
-amount of an agent that kills 50% of animals in test group
Immunopathogenesis
-when immune response to a pathogen is contributing cause of pathology & disease
Infection Cycle
-route of transmission of an infectious organism
-horizontal transmission - from 1 organism to another in same generation
-vertical transmission - from mom to fetus
Steps to Pathogenesis
- Exposure to Pathogens
- Adherence to skin or mucosa
- Invasion through epithelium
- Multiplication; growth & production of toxins & virulence factors
- Toxicity or Invasiveness
- Tissue/Systemic damage
1-4 are infection process, 5-6 are disease process
To cause disease, all pathogens must:
-attach to our surfaces & tissues
-damage tissues to obtain nutrients & replicate
-avoid host immune responses
Virulence Factors
-encoded on virulence genes
-include toxins, attachment proteins, capsules, & other devices
Pathogenicity Islands
-most appear to have been horizontally transmitted via conjugation or transduction
-unique GC/AT ratio
-codon bias
-flanked by inverted repeats
-found only in certain strains
Adhesins
-recognize specific receptors
-specifically bind to receptors on cell surface
-glycoproteins or lipoproteins found of pathogen surface, enabling binding to host cells
Pili or Fimbriae
-hairlike appendages that attach to specific host cells
-Type I - adhere to carbs on host membranes, grow from outer membrane of gram - bacteria
-Type IV - involved in twitching motility, retractable, can drag itself around, grown from inner membrane of gram - bacteria
Nonpilus Adhesins
-bacterial also possess adhesins that are not pili
-examples:
–M protein in Strep pyogenes
–Pertactin in pertussis
–MAM7 in pseudomonas aeruginosa
Why can some people be susceptible to infections?
-Immunocompetence: capacity to see & eliminate danger
-Receptor availability
-pathogens rely on specific surface receptors to recognize & bind
–differences in these from person to person
Capsules
-forms thick coating outside plasma membrane & cell wall
-serves 2 important functions in bacterial pathogenicity
–no capsule, strain is not pathogenic
–sticky & contains specific receptors to facilitate attachment to host
–inhibits opsonization & phagocytosis
Colonization
-growth of microorganisms after they’ve gained access to host tissues
Invasiveness
-ability of pathogen to grow in host tissue @ densities that inhibit host function
Septicemia
-bloodborne systemic infection
Hyaluronidase
-breaks down host tissues
Coagulase & Streptokinase
-manipulate clotting
-coagulase forms clots
-streptokinase breaks them down
Exotoxins
-proteins produced & secreted by various types of bacteria
-kill host cells & unlock nutrients
-AB toxins, cytolysins, superantigens
-mostly gram +
Endotoxins
-part of LPS of gram - bacgeria
-lipoteichoic acid on gram + cells
-hyperactive host immune systems to harmful levels
-mostly gram -
Membrane Disruption (cytolysins)
-2 types of exotoxins disrupt host cell membranes
-pore forming proteins
-phospholipase enzymes
Phospholipase enzymes
-hydrolyze phospholipids into fatty acids
Pore-forming proteins
-insert themselves into membranes by binding cholesterol & membrane receptors
Hemolysins
-lyse RBCs
Leukocidins
-lyse WBCs
AB exotoxins
-consist of 2 subunits that work together
-A subunit: toxicity associated factor
-B subunit: binds host cell, delivers A subunit
Endotoxin (LPS)
-made only by gram - bacteria
-LPS composed of lipid A (endotoxin), core glycolipid, and polysaccharide chain (o antigen)
-form on outer membrane
-as bacteria die, release MAMP that binds to macrophages/B cells
–triggers massive cytokine release, leading to fever, shock, inflammation, & death
Lipid A
-endotoxin part of LPS
-less toxic than exotoxins
-less immunogenic
-local infections, diarrhea, vomiting & fever
-immunopathogenic: sends immune system in spiral
Secretion systems
-facilitate cellular activities
-forms channels through membranes
-secretes proteins directly outside cells into env. or injects into host cell
Type II Secretion System (T2SS)
-modification of type IV pilus biogenesis
-extend & retract, like pili
-proteins get secreted into periplasm, then folded & secreted via outer membrane pore
Type III Secretion
-injection machine
-insert own receptors into target cells
-reenginerred flagellar synth mech
-triggered by cell-cell contact
-inject toxins (effectors) into euk. cells
Effector proteins
-proteins that have a function that will help bacteria manipulate host to it’s advantage
Type IV Secretion
-evolutionary modification of conjugation pilus that secretes proteins only, or proteins + DNA
-allows bacterial pathogens to secrete proteins directly from cytoplasm or periplasm
